Transcript Variation and Selection

Variation
Types of variation
• Variation means differences between species
(remember dichotomous key) or differences
within a species
• Types of variation:
1. Continuous variation
2. Discontinuous variation
Continuous variation
• Variation with a continuous range of unit, such
as the range of weight from light to heavy.
• Determined by genes and other factor such as
nutrition and activity (environment)
• Example: length of leaves or stems
range of height from shortest to
tallest
There are no clear divisions between the
intermediates
Discontinuous variation
• Variation in a limited number of phenotypes
with no intermediates.
• Example: various human blood type
different color of flower
ear lobe
Inheritance versus Variation
• Identical twins develop from the
same embryo and are genetically
identical. However, they are
different in many ways!
how this is happen?
Inheritance versus Variation
• A Mexican hat plant reproduce
asexually to make lots of tiny
plantlets all around its leaves. How
you would investigate the
environmental factor that effect the
variety of this plant?
Mutations
Mutation
• It is a change in a gene or a chromosome that
may cause a change in a phenotypic
characteristic
• Mutation can be harmful but some are
beneficial and some have no effect
Gene mutation
• Mutation of the red color eye of a fruit fly into
white eyes. It is caused by the changes of gene
that no longer coded for the production of the
red pigment.
• Albino, mutation of melanin pigment that
responsible to protects skin and eyes from
ultra violet light. The gene can mutate and
stop produce melanin. This trait is a recessive
allele and albino is a homozygous recessive.
Gene mutation
• Sickle cell anemia (SCA) is an inherited disease
of the blood. It’s the result of an allele that
causes the abnormality form of haemoglobin
(C shaped of red blood cell ) which makes it
difficult for the red blood cells to carry oxygen.
Chromosome Mutation
• Down syndrome, is a mutation that occurs
during meiosis when two of the chromosomes
do not separate properly. Instead of the egg
having 23 chromosomes there is an extra
chromosome.
• If the egg is fertilised the baby will have 47
chromosome
• Down’s syndrome affects about 1 in 1000
babies
Meiosis KM
12
Causes of mutation
• Damage to DNA or failure in the copying
process before nuclear division
• Mutation occur naturally at random but is
increased by exposure to radiation, such as:
ultra violet, X rays and gamma rays
• Mutation also increased by some dangerous
chemicals, such as: benzpyrine in cigarette
smoke.
Effect of Mutation
• Mutation may lead to cancer (as happened
after atomic bomb in Japan and the nuclear
power station in Chernobyl in the Soviet
Union)
• Mutation on red blood cell and cause
heterozygous cause resistance to malaria and
since they still have normal red blood cell they
do not have problem in transporting oxygen.
Natural Selection
• The process by which organisms that
are well adapted to their
environment have a greater chance
to breed and pass on their genes to
the next generation than those that
are less well adapted
The process of natural selection
• Variation
• Over population
• Competition
• Adaptation
• Evolution
Search from the Biology book or article
to explain how the process above may
lead to the natural selection